Biomedical science最新文献

The antibiotic bleomycin was examined as a possible component of hybrid molecules composed of an address fragment and a generator of reactive oxygen species. The bleomycin-Fe(II) complex was found to destroy the erythrocyte membrane by generating reactive oxygen. The ability of antioxidants to slow down haemolysis points to a free-radical mechanism for this process. The protective effects of catalase and superoxide dismutase indicate that hydrogen peroxide and the superoxide radical formed on autoxidation of the complex are essential for membrane damage. Haemolytic activity is also exhibited by bleomycin-Fe(III) reduced in the NADPH-cytochrome P450 reductase reaction. The covalent binding of bleomycin to such address molecules as concanavalin A and antierythrocyte immunoglobulin G enhances the ability of the bleomycin-Fe(II) complex to destroy the plasma membrane of erythrocytes.

A ubiquitous mammalian transcription factor, Oct-1 (also known as OTF-1, NF-A1, OBP100, or NFIII), stimulates the initiation of replication of adenovirus DNA, and may also be involved in the activation of some chromosomal replication origins. If this is true, binding sites for Oct-1 should be present within regions responsible for the initiation of DNA replication. In this study such a binding site has been identified within a 340bp fragment that was originally isolated from a minor fraction of DNA associated with a complexed form of DNA polymerase alpha from nonregenerating rat liver, and which shows autonomous replication sequence activity in a transient transfection assay. Northern blot analysis was used to show that Oct-1 mRNA is induced in regenerating rat liver 6-14 h after hepatectomy.

The interaction of liposomes containing different amounts of cholesterol with low-density lipoproteins from human serum was investigated. The efficiency of the interaction was found to depend on the cholesterol content of the liposomes and was highest for liposomes with the maximum cholesterol:phospholipid molar ratio. These liposomes selectively and effectively interacted with low-density lipoproteins; up to 90% of lipoprotein particles interacted with liposomes in serum. Fusion of particles with liposomes was observed during the interaction.

Intracerebroventricular administration of various doses of neuropeptide Y (NPY) to rats had different effects on their feeding behaviour: the lowest dose (100 ng) decreased food intake, but higher doses (5 micrograms) markedly increased the intake. Prazosin, a selective blocker of alpha 1-adrenergic receptors, suppressed the effect induced by 5 micrograms (but not 100 ng) NPY. No such effect was observed with injections of yohimbine or propranolol. The opiate receptor antagonist, naloxone, blocked the feeding behaviour induced by 5 micrograms NPY without having any other effects on the responses induced by 100 ng NPY. The data obtained testify to heterogeneity within the NPY receptors of the central nervous system. It is concluded that the effects of high doses of NPY on feeding behaviour are mediated, at least in part, by alpha 1-adrenergic receptors.

A flow-injection method for the determination of glucose in serum is presented. It is based on the enzymatic measurement of oxygen consumption detected via oxygen quenching of the luminescence of certain metalloporphyrins. Phosphorescent water-soluble Pt2+ and Pd(2+)-porphyrins have been characterized by luminescence spectroscopy and decay-time measurements in various buffers, and found to be suitable for oxygen detection in biological systems. A new method for the flow-injection analysis of glucose has been developed based on the use of a column of immobilized glucose oxidase and the indicators Pt(2+)-coproporphyrin III and Pd(2+)-coproporphyrin I. The system has been optimized for glucose determination in aqueous samples and in whole serum with the 0.5-200 mM glucose range. Twenty assays can be performed in an hour, and the system has potential for commercial development with biotechnological and medical applications.

Enzyme preparations of Rous sarcoma virus (RSV) reverse transcriptase have been isolated from a culture of E. coli HB101(pMF14). The enzyme has been purified to homogeneity and been shown to consist of two subunits, of molecular mass 97.4 and 61.3 kDa, respectively. The optimum conditions for the DNA polymerase and RNAase H activities, fidelity of DNA synthesis on a homogeneous RNA template, and the inhibitory effect of azidothymidine triphosphate have been determined. Data on the use of RSV recombinant reverse transcriptase for cDNA synthesis are given.

Three kinds of monoclonal antibody (Mab) of different specificity have been obtained against the N-terminal disulphide knots of fibrinogen and fibrin. Their effects on different phases of fibrin polymerization have been studied. These antibodies were shown to be directed against different epitopes of the B beta(1-53) fragment of the fibrinogen molecule. The different Mab had different effects both on the rate of protofibril lateral aggregation and on the final turbidity of fibrin clots. The Mab were of three specificities: (1) those from clone 2d-2a inhibited the rate of lateral aggregation of protofibrils and decreased the turbidity of the final clot; (2) those from clone B-4C accelerated the polymerization step but did not affect clot turbidity: and (3) those from clone D-IB did not have any effect on either fibrin polymerization or final clot turbidity. The localization of the epitopes recognized by all three kinds of Mab and analysis of our own data and those of others allow us to conclude that one of the active loci involved in protofibril lateral association is situated in the B beta(15-53) fragment of the fibrinogen molecule. Fibrinopeptide B does not need to be split off for this site to function. Fibrin polymerization can occur when one of the two sites of protofibril lateral aggregation in dimeric fibrin molecules is blocked by Mab, and the final clot turbidity is then reduced. The splitting off of one of the two fibrinopeptides B in fibrinogen molecules by thrombin can take place even when the second B beta(Arg14-Gly15) bond is blocked by an antibody molecule.(ABSTRACT TRUNCATED AT 250 WORDS)

An epitope of human leukocyte alpha interferon A (IFN-A), which is recognized by the murine monoclonal antibody NK2, has been mapped by using four successive approaches. Limited proteolysis of the IFN-A chain, followed by electrophoresis, Western blotting, and probing of the proteolytic fragments with NK2 showed that an epitope was located within the sequence residues 110-140. A panel of human IFN subtypes bearing substitutions within the sequence 110-140 was tested for reactivity with NK2 in enzyme-linked immunosorbent assays. The results from these assays suggested that the epitope is within the sequence 112-121. Analysis of a hybrid protein IFN-A(1-92)/F(93-166) revealed that the N-terminal region of IFN-A played no significant role in NK2 binding. Three residues of IFN-F (Asn113, Val114, and Lys121) were substituted for the corresponding residues from IFN-A (Lys113, Glu114, and Arg121) by site-directed mutagenesis of the gene encoding IFN-F. NK2 was able to bind the mutated protein, IFN-F(A 113, 114, 121), as well as unmodified IFN-A. The data show that the epitope recognized by NK2 is located within the C-terminal region of IFN-A (residues 112-121). This epitope consists of the essential residues 114 and 116, and residues 112, 113, 115, 117, and 121 presumably contribute the configuration of the epitope.

Epileptogenic foci were formed in rabbit visual cortex by freezing with liquid nitrogen. RNA isolated from the epileptogenic cortex (RNAepl), or from the frontal lobes (RNAcont) was injected into spontaneously active neurons of the mollusc Planorbarius corneus. The amplitude and duration of the spontaneous action potentials generated following the injection of RNAepl were reproducibly higher than those produced following the introduction of RNAcont. But the time interval between injection and cessation of spontaneous activity was considerably shorter after RNAepl-injection than after RNAcont-injection. Perfusion of neurons with a solution containing puromycin substantially prolonged the period of spontaneous discharge generation in both cases. The addition of Co2+ to the perfusion solution restored the spontaneous rhythmic activity to cells in which the generation of spikes had ceased following the injection of RNAepl. The mechanism underlying these effects is discussed.